Photoconductive zinc oxide compositions comprising oxonol, hemioxonol, or benzylidene dyes



Feb. 11, 1964 J. E. JONES ETAL 3,121,008

' PHOTOCONDUCTIVE ZINC OXIDE COMPOSITIONS COMPRISING OXONOL, HEMIOXONOL, OR BENZYLIDENE DYES 4 Filed April 9, 1959 Fig 300 400 500 600 700 m ,0 A 5 p DIME 7' H YLAM/IVOCl/V/VAMYL/DEWE 2 THIOBARB/TUH/C ACID Fig. 2

8 Hll mw 1| IIII WWI NH 300 400 500 600 700 my a [ZMLO/VO/V/Tfi/Lj [Z- THIOBARB/TUR/C lac/0] TRIMETH/NE- OXO/VOL Fig. 3

JEAN E JONES PAUL l1. STEWART INVENTORS BX /M W W ATTORNEYS Filed Apr. 9, 1959, Ser. No. $95,157 10 Claims. (Cl. 96-1) This invention relates to sensitized photoconductive compositions and layers comprising zinc oxide which are particularly useful in the document copying field.

This application is a continuation-in-part of U.S. application Serial No. 645,419, filed March 12 1957 now abandoned, by Paul H. Stewart.

It is known that zinc oxide can be employed in rnalrinphotoconductive layers which can be coated on ordinary paper, and that photographic copies can be conveniently prepared from these photoconductive materials. This process 18 somewhat related to the system known as xerography, in that a photoconductive element is 'ven a uniform charge, usually from a corona dischar e followed by exposure to an image using radiation a? which the photoconductive composition is sensitive. This exposure causes an imagewise discharge of the change on the surface of the photoconductive composition (the electrostauc charge leaking away from the surface roughly in proportion to the amount of radiation received, as described below), so that the portions of the surface retaming their charge can then be treated with a charged powder or toner of opposite charg This powder or toner 1S attracted to the portions of the surface retainin a charge, thus giving a visible copy which may be fixed in a number of various ways to the surface, or alternatively, transferred to another sheet or surface which provides the permanent copy.

In the known system of employing zinc oxide in photoconductive layers, a relatively conducting support, such as paper, is coated with a photoconductive zinc oxide dispersed in an electrically insulating binder material. The grounded support is then placed beneath a corona discharge so that a blanket negative electrostatic charge on the zinc oxide surface is accumulated. Inasmuch as the zinc oxide is a photoconductive material, it is necessary to perform this charging separation in the substantial absence of any ultra-violet or visible radiation. The charged ZIIIC oxide photoconductive layer can then be exposed to a photographic image in the usual manner, the portions of the zinc oxide which receive light or ultra-violet radiatron losing wholly or in part (depending upon the extent of exposure), the negative electrostatic charge, while the unexposed or partially exposed portion-s of the charged layer retaining their negative electrostatic charge. The resulting latent image can then be developed to a visible image by means of a pigment powder which has a charge opposite to the negative charge remaining on the areas of the photoconductive layer. The pigment powder is thus strongly attacted to the negatively charged areas and can be permanently afiixed to the surface of the photoconductive layer by simply melting the vehicle for the powder at some temperature below the charring temperature of the paper support.

One of the disadvantages of the zinc oxide normally used in photoconductive layers is that the sensitivity is not primarily within the visible region of the spectrum, so that such materials have a relatively low speed when an ordinary light source, such as a tungsten lamp or flucrescent lamp, is used as the exposing source. The zinc oxide normally employed in such photoconductive layers has its greatest sensitivity in the ultra-violet region of 3,121,908 Patented Feb. 11, 1964 the spectrum, and normal light sources have very weak radiation in this region. While various sensitizing matetrials have been suggested to increase the sensitivity of zinc oxide in the visible region of the spectrum, so that the zinc oxide has some panchromatic or orthochromatic sensitivity, many of these dyes are unsatisfactory since they must be used in such large amounts to obtain optimum sensitivity that the surface of the paper takes on a very strong coloration which reduces the contrast of the desired image and has an undesirable esthetic effect. For example, it has been previously suggested to use organic dyes such as Rose Bengal to increase the sensitivity of the zinc oxide, but this material has a very strong coloration so that the undesirable effects mentioned above are quite evident.

It is, therefore, desirable to have a means of increasing the sensitivity of zinc oxide compositions to conventional light sources, such as tungsten light, without seriously affecting the coloration of the photoconductive surface. Moreover, it is desired to have more effective sensitizing means so that shorter exposure times can be employed in the reproduction of graphic originals. It is also desired to have zinc oxide photoconductive compositions which have sensitivity to particular wavelengths of radiation so that the photoconductive compositions can be used in the manufacture of color materials.

An object of our invention is to provide a convenient means of increasing the sensitivity of photoconduotive zinc oxide layers to visible radiation. Another object is to provide photoconductive zinc oxide layers which have much higher speeds than those previously available. Still another object is to provide a means for sensitizing photoconductive zinc oxide compositions to particular regions of the spectrum so that these compositions can be used in the manufacture of color materials. Other objects will become apparent from a consideration of the following description and examples.

The following invention relates to the discovery that certain oxonol, hemioxonol or benzylidene dyes containing a mercapto group can be used to usefully extend the sensitivity of photoconduct-ive zinc oxide compositions and thus markedly increase their speed to white light or any other exposing source emitting radiation in the region to which the dyes of our invention sensitize the zinc oxide. The dyes of our invention which have been found particularly useful contain a heteroeyclic nucleus which contains an enolizable NHC group, as a portion of the heterocyclic ring. It has been found that dyes containing a substituent on the aforementioned nitrogen atom do not provide results comp-arable to those obtained with dyes having a hydrogen atom attached to the nitrogen atom. The hydrogen atom attached to the nitrogen atom can readily migrate to the sulfur atom of the adjacent thiccarbonyl group to provide a mercapto group. While such dyes have been previously used to sensitize silver halide compositions, they have not found wide use in the photographic field because of their relatively poor sensitizing action for silver halides. It was, therefore, unexpected to find that such dyes could be used to extend the sensitivity of zinc oxide to an extent many times that obtainable with more conventional spectral sensitizing dyes, such as the N-substituted merocyanine, oxonol, hemioxonol and benzylidene dyes.

The effect of our dyes on photoconductive zinc oxide compositions is graphically shown in the accompanying drawings wherein the curves in FIGURES 1-3 represent the sensitivity of photoconductive zinc oxide compositions sensitized with polymethine dyes according to our invention. Further details regarding such sensitizing action are' given below;

The dyes which can be usefiully employed in our invention comprise many dyes which have been used previously in silver halide photography, although it is well known to those skilled in the ant that many such dyes have few advantages in increasing the sensitivity of silver halide emulsions. Accordingly, many of these dyes frequently find their maximum utility as light-absorbing dyes in the preparation of filter layers for multilayer materials, or in antihalation layers.

Dyes containing an enolizable s NH group as a part of the ketomethylene acidic nucleus, include those dyes represented by the following general formula:

wherein R represents a hydrogen atom, an alkyl group (e.g., 'methyl, ethyl, propyl, butyl, fl-hydroxyethyl, ethoXycarbonylrne-thyl, etc.), or an aryl group (eg phenyl, o-, m-, and p-tolyl, o-, m-, and p-chlorophenyl, etc.), R represents an amincaryl group (e.g., p aminophenyl, p-dirnethylaminophenyl, p-diethylaminophenyl, etc.), or an aryl group, such as an oxyaryl group (e.'g., p-rnethoxyphenyl, p-ethoxy-phenyl, 3-ethoxy-4-hydroxyphenyl, etc.), or a heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring, such as heterocyclic nuclei commonly found in oxonol dyes, n represents a positive integer of from 1 to 3 and X represents an oxygen atom, a sulfur atom, a

group or a I ll group, wherein R and R each represents a hydrogen atom, an alkyl group (e.g., methyl, ethyl, propyl, butyl, amyl, heptyl, octyl, fi-methoxyethyl, etc.), or an aryl group (e.g., phenyl, o-, m-, and p tolyl, 0-, m-, and p-chlorophenyl, etc.), provided at least one of the groups R, R or R represents a hydrogen atom (so that said dye contains an enolizable Typical heterocyclic nuclei defined by R; of Formula I above include, for example, heterocyclic nuclei containfrom 5 to 6 atoms in the heterocyclic ring, such as a pyrazolino-ne nucleus (e.g., 3-methyl-1-phenyl-2-pyrazolin-S-one, 1-phenyl-2-pyrazolin-5-one, l-(2-benzothiazolyl)-3-me=thyl-2-pyrazolin-5-one, etc.), an isoxazolinone nucleus (erg, 3-phenyl-2-isoxazolin-S-one, 3-methyl-Z-isoxazolin-S-one, etc.), an oxindole nucleus (e.g., l alkyl-2,3-dihydro-2-oxindoles, etc.), a 2,4,6-triketohexahydropyrimidine nucleus (erg, barbituric acid or Z-thiobarbitu'ric acid, as Well as their l-alkyl (e.g., l-methyl, l-ethyl, l-mpropyl, l-n-heptyl), etc.), or 1,3-dialkyl (e.g., 1,3-dirnethyl, 1,3-diethyl, 1,3-di-n-propyl, 1,3-diisopropyl, 1,3-diczyclohexyl, 1,3-di(fl-methoxyethyl), etc.), or 1,3-dianyl (e.g., 1,3-d-iphenyl, l,3-di(p-chlorophenyl), 1,3-di(pethoxycarbonylphenyl), etc.), or l-aryl (e.g., l-phenyl, l-p-chlorophenyl, 1-p-ethoxycarbonylphenyl), etc.), or l-alkyl-S-aryl (e.'g., 1-ethyl-3-phenyl-1, n-heptyl-3-phenyl, etc.) derivatives), a rhodanine nucleus (i.e., 2-thio-2,4- thiazolidinedione nucleus), such as rhodanine, 3-alkylrhodanines (e.g., 3-ethylrhodanine, 3-allylrhodanine,

etc.), or 3-arylrhodanines (e.g., 3-phenylrhodanine, etc.), etc, a 2-thio-2,4-oXazo-lidinedione nucleus (i.e., a 2-thio-2,4(3H,5H)-oxazoledione nucleus) (e.g., 3-et-hyl- Z-thio-Z,4-oxazolidinedione, etc.), a thianaphthenone nucleus (e.g., 3(2H)-thianaphthenone, etc.), a 2-thio-2,5- thiazol-idinedione nucleus (i.e., a 2-thi0-2,5(3H,4H)-thi' azoledione nucleus) (e.g., 3-ethyl-2-thio-2,5-thiazolidine-- dione, etc.), a 2,4-thiazolidinedione nucleus (e.g., 2,,4-thi-- azolidinedione, 3-ethyl-2,4-thiazolidinedione, 3-phenyl 2,4-thiazolidinedione, 3-a-naphthyl-2,4-thiazolidinedione,.

etc.), a thiazolidinone nucleus (e.-g., 4-thiazolidinoue dinedione, 1 -ethyl-3-a-naphthyl-Z-thio-2,4-imidazolidine- 1,3=dipheny1-2-thio-2,4-imidazolidinedione, etc.),

dione, a 2-imidazolin-5-one nucleus (etg, 2-n-propylmercapto Z-imidazolin-S-one, etc.), etc.

Another group of dyes containing a mercapto group which can advantageously be employed in our invention is the class of dyes represented by the following general formula: t

t 1 s=o 0:0 c-oH=cH R,

wherein R and X each have the values given above, Q represents the atoms necessary to complete a cyelohexene ring (which can have substituted thereon simple substituents, such as methyl, ethyl, etc.) and R; repre- 'sents an aryl group, such as the oxyaryl groups definedi by R above, or alternatively, R can represent a hetero-- cyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring, as defined above by R Useful oxonol dyes embraced by Formula 1 above include those dyes represented by Formula Ia: (Ia) I! (I? on r t s=0 /0=oH(oH=oH)n-1o wherein R, X and it each have the values given above,

R re resents a hydrogen atom, an alkyl group (including the alkyl groups defined by R above) or an aryl group (including the aryl groups defined by R above) and X represents a hydrogen atom, a sulfur atom, a .I]\]. Ra

group or a II I 0R group, wherein R and R each represents a hydrogen atom, an alkyl group (e.g., methyl, ethyl, propyl, butyl, amyl, heptyl, octyl, fi-rnethoxyethyl, etc.), or an aryl group (cg, phenyl, o-, In, and p-tolyl, o, 121-, and pchlorophenyl, etc.), etc.

Another group of dyes useful in practicing our invention are those dyes embraced by the following general formula:

U.S. Patent 2,216,441, Keyes, granted October 1, 1940 U.S. Patent 2,241,238, Brooker et al., granted May 6, 1941 U.S. Patent 2,345,193, Gaspar, granted March 28, 1944 British Patent 396,646, I.G.F.A., accepted August 10, 1933 British Patent 428,359, Kendall, accepted May 3, 1935 British Patent 624,462, Gevaert, accepted June 9, 1949 As shown by the above formulas, the dyes of our invention can contain substituents common to dyes in the cyanine dye art.

Typical dyes useful in practicing our invention include those dyes represented by the following formulas:

The above spectral sensitizing dyes can be combined with the zinc oxide photoconductive material in any convenient manner. For example, the spectral sensitizing dye can be added to the zinc oxide composition while dissolved in an organic solvent. Pyridine, methanol, ethanol, acetone, etc., can be used to dissolve many of the dyes useful in practicing our invention. The zinc oxide can be uniformly dispersed in an organic solution of the binder customarily employed for the zinc oxide and a solution of the sensitizing dye added to this coating solution. After thorough mixing, the sensitized composition can be coated on a paper support and dried in the usual manner.

Alternatively, an unsensitized zinc oxide coating can be prepared as described above and after removal of the organic solvent, the paper coating can be immersed in a solution of the sensitizing dye. This method has been found to be particularly useful in that higher speeds can be frequently obtained.

The binders for the zinc oxide comprise many of the resinous compositions which are commercially available. Such resins are sold under trade names, such as Plaskon ST-856, Rezyl 405-18, Pliolite S-7 or S-D, Styresol 4440, DC 804, etc. These resins comprise styrenebutadiene copolymers, silicone resins, styrene-alkyd resins, silicone-alkyd resins, soya-alkyd resins, polyvinyl chloride, polyvinyl acetate, etc. The methods of making such resins have been previously described in the prior art. For example, styrene-alkyd resins can be prepared according to the method described in Gerhart US. Patent 2,361,019, issued October 24, 1944; Rust U.S. Patent 2,258,423, issued October 7, 1941; Kropa US. Patent 2,453,665, issued November 9, 1948, etc. Other binders, such as paraflin, mineral waxes, etc., can also be employed. These binders are generally characterized as having marked hydrophobic properties (i.e., being substantially free of any water-solubilizing groups, such as hydroxyl, free acid groups, amide groups, etc.) and as being good electrical insulators or as having high electrical resistivity. These binders can be easily dissolved in organic solvents having a boiling point below the charring temperature of the paper support. Also, these binders have the desirable property of readily dispersing the zinc oxide photoconductive material. Some resinous binders are relatively poor insulators and do not provide coatings which can be stored for prolonged periods of time after the photoconductive coatings have been negatively charged. This is particularly noticeable at relatively high humidities, and the photoconductive coatings should be charged shortly before use in such instances; that is, it is not advisable to charge the photoconductive coatings too long in advance before use. Such problems are well understood by those skilled in the art.

Non-polar solvents have been found to be particularly useful in preparing the photoconductive layers in that any residual solvent which cannot be removed does not have a deleterious effect on the keeping qualities of the photoconductive layers. Such solvents include the aromatic hydrocarbons, such as benzene, xylenes, toluene, etc.

The zinc oxide employed in our invention should generally consist of relatively small particles of less than 0.5 micron mean diameter. Such zinc oxide materials are readily available and can be purchased under a variety of trade names, such as Protox No. 168 (New Jersey Zinc Company), etc. Sufficient binder should be employed to insulate each of the zinc oxide particles from the surrounding particles in the composition. The most useful or optimum quantity of zinc oxide to binder for a particular binder can be readily determined by making a series of test coatings wherein the quantity and relative amounts of zinc oxide to binder are employed.

Exposure of the charged photoconductive layer to visible radiation or ultraviolet radiation causes a loss or reduction of the negative charge in those portions of the photoconductive material which are exposed to the radiation. The degree of loss will depend on the intensity and time of exposure to the radiation, in general. The resulting latent electrophotographic image can then be developed to a visible image in a variety of ways, including those which have been previously employed in electrophotographic processes, such as xerography. A particularly useful means of developing the latent electrophotographic image comprises use of a magnetic brush. This magnetic brush development makes use of a ferromagnetic powder", such as iron filings, which has been intimately mixed with pigmented resin, or sulfur. magnetic powder and pigmented resin results in a tri b0 electric effect wherein the pigmented resin acquires an electric charge depending upon the relative position of the resin to the ferromagnetic powder in the triboelectric series. That is, ordinary iron powder is below most resins in the triboelectric series, and mixture with a resin higher in the series results in the depostion of a positive electrostatc charge on the resin. The resulting mixture can then be picked up by a magnet on which the iron particles, or other ferromagnetic powder, arrange themselves in the conventional pattern, so that the long chains of filings resemble an ordinary brush. This magnetic brush can then be placed in contact with the exposed photoconductive layer and the brush passed across the negative electro static latent image which is on the surface of the photoconductive material. As the magnetic brush passes over the areas of the photoconductive material which have residual negative charge thereon, the electrostatic attraction between the charged pigmented resin particles and the oppositely charged image areas in the photoconductive material is greater than the attraction between these particles and the ferromagnetic powder, so that the pigmented resin is deposited on the surface of the photoconductive material roughly in proportion to the residual charge on the surface of the photoconductive layer. By electing a resin with a low melting point, the developed image can then be fixed to the surface of the paper by heating to a temperature above the melting point of the resin, but below the charring temperature of the paper. The resin in the pigmented resin compositions can be varied, depending upon the effects desired and the type of copy which is being reproduced. Such resins may be the same as those employed in the insulating layer coated on the paper support, such as styrene-butadiene resins, etc. The particle size of the pigmented resin used in development can vary, although the range of 0.1 to 25 microns is adequate for most purposes. Various pigments can be used in the resin developing compositions. The ability of the pigmented resin to accept a positive charge is dependent upon the type of resin selected. The pigment l merely serves to impart color to the resin and probably imparts very little, if any, influence on the overall charge of the pigmented resin.

The following examples will serve to illustrate the manner of using the optically sensitizing photoconductive materials of our invention.

A series of dyes represented by the above numbers were dissolved in a suitable solvent, such as acetone, pyridine, methanol, etc., depending upon the solubility characteristics of the particular dye, and separate sheets of paper coated with unsensitized zinc oxide compositions were immersed for about 15 seconds in these solutions containing the sensitizing dyes.

papers were then dried in air in a vertical positon. After drying the paper strips were exposed to a 10,000-volt' corona discharge for 15 seconds and then exposed to tungsten illumination for 2 seconds in an intensity scale sensi tometer and spectograph'. The exposed coatings were then developed by the magnetic brush technique described.

above using small iron particles dispersed in black pigmerited sulfur. Finally, the images were fixed by fusing the developed image to the paper at a temperature of about C. A duplicate strip was treated in the same manner with the sensitizing dye being omitted from l the sensitizing solution. This served. as a control, the speed of which was arbitrarily set at one. In the following table the dyes are identified by number and in terms of their concentration in the sensitizing solution. The

Agitation of the ferro- The sensitizing zinc oxide memes relative speed, as compared to the control, sensitizing maximum and range, are also given.

The accompanying drawing will serve to illustrate schematically the efiect of several of our sensitizing dyes in extending the sensitivity of photoconductive compositions.

In FIGURE 1, the solid curve represents the sensitivity of a photoconductive zinc oxide sensitized with -p-dimethylaminocinnamylidene 2 thiobarbituric acid. The sensitizing data for this dye are given in the above table, dye 1.

In FIGURE 2, the solid curve represents the sensitivity of zinc oxide sensitized with [malononitrile] [Z-thiobarbitun'c acidJtrimethineoxonol. The sensitizing data for this dye are given in the above table, dye 11.

In FIGURE 3, the solid curve represents the sensitivity of a photoconductive zinc oxide sensitized with bis[2- thiobarbituric acidJpentamethineoxonol. The sensitizing data for this dye are given in the above table, dye 8.

It has also been found that the sensitizing dyes of our invention can be usefully employed to extend the sensitivity of zinc oxide material intended for use in a photoconductographic process. Photoconductographic processes have been previously described in the prior art, such as in Bronk British Patent 188,030, accepted October 23, 1922, and Hana Dutch Patent 5,142, patented June 13, 1920.

The following examples will serve to illustrate the method of using the sensitized zinc oxide compositions of our invention in a photoconductographic process.

Dyes 1, 2, 8, 9 and 10 were separatelydissolved in a suitable solvent and mixed with a composition comprising photoconductive zinc oxide and a resinous, insulatorbinder comprising a synthetic resin, such as Pliolite S7 (a styrenebutadiene copolymer), the concentration of the dyes being 5.6 micromoles per 56 grams of zinc oxide. The zinc oxide to binder ratio was 3:1. A solvent mixture comprising 95% toluene and 5% methanol was added to give a mixture containing solids by weight, and the solutions were separately coated at a thickness of 0.010 inch, Wet, on paper-backed aluminum foil.

Each of the coatings was then dried and exposed in the customary manner to daylight-quality radiation in a high intensity wedge spectograph. The exposed coatings were then developed by contacting the exposed surface with a viscose sponge wet with a developer solution comprising sodium thiosulfate saturated with silver chloride. The viscose sponge was held at a potential of about 70 volts positive with respect to the aluminum foil backing. The sensitizing data for each of the coatings was approximately the same as indicated in the above table for coatings obtained in an electrophotographic process. For example, dye 1 gave a sensitizing maximum of about 610 m with sensitivity extending from about 480 to 680 mu.

As indicated above the sensitizing dyes of our invention 10 can be prepared according to methods which have been previously described in the prior art. For instance, dye 11 above can be prepared by reacting a Dains et al. type intermediate, e.g. 5-(3-acetanilidoallylidene)-2-thiobarbituric acid, with malononitrile in the presence ofa basic condensing agent.

The sensitizing dyes of Formula II above can advantageously be prepared by condensing the intermediates obtained by reacting isophorone-type compounds with a heterocyclic compound containing a cyclic ketomethylene group, with an aromatic aldehyde, which can contain conventional substituents, such as amino, hydroxyl, alkoxyl, etc. For example, Compound 14 above was obtained by condensing isophorone with 2-thiobarbituric acid in the presence of a basic condensing agent, followed by condensation of the resulting intermediate with p-dimethylaminobenzaldehyde.

The compounds of Formula I above wherein R represents an aryl group can be obtained by condensing together a heterocyclic compound containing a cyclic ketomethylene group with an aromatic aldehyde, such as benzaldehyde, cinnamaldehyde, etc., suitably substituted on the benzene ring by an amino group, hydroxyl, alkoxyl, etc. Certain of the dyes of our invention, particularly the dyes represented by Formula Ia above form salts, such as sodium salts, potassium salts, ammonium salts (including organic ammonium salts), etc. It is to be understood that the dyes of Formula Ia can, therefore, be used either in the form depicted above, or in the form of their alkali metal or ammonium salts.

The compounds of Formula I above wherein R represents an arylamino group can be prepared by condensing together a Dains et al. type intermediate with an aromatic primary amine, such as aniline, p-hydroxyaniline, etc. By Dains et al. type intermediates, we mean intermediates of the type represented by Formula III in Van Lare and Brooker U.S. Patent 2,548,571, issued April 10, 1951.

Compound 17 above was prepared by condensing rhodanine together with p-nitroso-N,N-diethylaniline. Other p-nitroso-N,N-dialkylaniline can be reacted in like manner with other cyclic ketomethylene compounds, such as thiobarbituric acid, etc.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected Within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What we claim as our invention and desire secured by Letters Patent of the United States is:

1. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binder-insulating material for said zinc oxide, said zinc oxide being sensitized with a dye selected from the class represented by the following general formula:

wherein R represents a member selected from the class consisting of a hydrogen atom, an alkyl group, and an aryl group, R represents a member selected from the class consisting of an aryl group, an alkoxycarbonylcyanomethylene group, an arylamino group, a dicyanomethylene group and a heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring, it represents a positive integer of from 1 to 3, and X represents a member selected from the class consisting of an oxygen atom, a sulfur atom, a

l 7. group and a group, wherein R and R each represents a member selected from the class consisting of a hydrogen atom, an alkyl group and an aryl group, provided that at least one of the members selected from the class consisting of R R and R represents a hydrogen atom.

2. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in'a high dielectric, organic binder-insulating material for said zinc oxide, said zinc oxide being sensitized with a dye selected from the class represented by the following general formula:

t e an n s=o C=CI-I(OH=CH)n-1 O C=S X X1 wherein R and R each represents a member selected from the class consisting of a hydrogen atom, an alkyl group and an aryl group, n represents a positive integer of from 1 to 3, X represents a member selected from the class consisting of an oxygen atom, a sulfur atom, a

group and a group, wherein R and R each represents a member selected from the class consisting of a hydrogen atom, an alkyl group and an aryl group, provided at least one of the members selected from the class consisting of R, R and R represents a hydrogen atom, and X represents a member selected from the class consisting of an oxygen atom, a sulfur atom, a

N in group and a group, wherein R and R each represents a member selected from the class consisting of a hydrogen atom, an alkyl group and an aryl group. I

3. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binder-insulating material for said zinc oxide, said zinc oxide being sensitized with a dye selected from the class represented by the fo1- lowin' general formula:

L II a positive integer of from l to 3, and X represents a member selected from the class consisting of an oxygen atom, a sulfur atom, a

1? Ed group and a group, wherein R and R each represents a member selected from the class consisting of a hydrogen atom, an

tized photoconduct-ive zinc oxide particles .liniforr'nly dispersed in a high dielectric, organic binder-insulating ma: terial for said zinc oxide, said zinc oxide being sensitized with a dye selected from the class represented by the fol lowing general formula:

R 0 I II F? s=o C=CH:(,OH=.GH)n1-Rl wherein R represents a member selected from the class consisting of a hydrogen atom, an alkyl group containing from 1 to 4 carbon atoms, and an aryl group containing from 6 to 7 carbon atoms, R represents an oxyaryl group containing from 6 to 8 carbon atoms, n represents .a positive integer of from 1 to 3, and X represents a member selected from the class consisting of an oxygen atom, a sulfur atom, a

group and 9.

group, wherein R and R each represents a member selected from the class consisting of a hydrogen atom, an alkyl group containing from 1 to 8 carbon atoms and an aryl group containing from 6 to 7 carbon atoms, provided at least one of the members selected from the class consisting of R, R and R represents a hydrogen atom.

5. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binderrinsulating material for said zinc oxide, said zinc oxide being sensitized with a dye selected from the class represented by the following general formula:

wherein R and R each represents a member selected.

group and a group, wherein R and R each represents a member selected from the class consisting of a hydrogen atom, an alkyl group containing from 1 to 8 carbon atoms and an aryl group containing from 6 to 7 carbon atoms, provided at least one of the members selected from the class consisting of -R, R and R represents a hydrogen 13 atom, and X represents a member selected from the class consisting of an oxygen atom, a sulfur atom, a

7. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binder-insulating material for zinc oxide, said zinc oxide being sensitized with a dye represented by the following formula:

8. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binder-insulating material for zinc oxide, said zinc oxide being sensitized with a dye represented by the following formula:

N-o H II 9. A photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binder-insulating material for zinc oxide, said zinc oxide being sensitized with a dye represented by the following formula:

10. A duplicating sheet comprising a paper support having coated thereon a photoconductive composition comprising sensitized photoconductive zinc oxide particles uniformly dispersed in a high dielectric, organic binderinsulating material for zinc oxide, said zinc oxide being sensitized with a dye selected from the class represented by the following general formula:

wherein R represents a member selected from the class consisting of a hydrogen atom, an alkyl group, and an aryl group, R represents a member selected from the class consisting of an aryl group, an arylamino group, an alkoxycarbonyl-cyanomethylene group, a dicyanomethylene group, and a heterocyclic nucleus containing from 5 to 6 atoms in the heterocyclic ring, n represents a positive integer of from 1 to 3, and X represents a member selected from the class consisting of an oxygen atom, a sulfur atom, a

group and a group, wherein R and R each represents a member selected from the class consisting of a hydrogen atom, an alkyl group and an aryl group, provided that at least one of the members selected from the class consisting of R, R and R represents a hydrogen atom.

References Cited in the file of this patent UNITED STATES PATENTS 2,937,944 Van Dorn et a1. May 24, 1960 FOREIGN PATENTS 428,222 Great Britain May 3, 1935 201,416 Australia Apr. 13, 1956 778,613 Great Britain July 10, 1957 OTHER REFERENCES CA. 43, 7349d (1949). (Copy in Sci. Lib.)

Young et al.: R.C.A. Review, pp. 469-484, Dec. 1, 1954. (Copy in Sci. Lib.)

Nelson Journal of the Optical Society of America, 46, No. 1, 13-16 (1956). (Copy in Sci. Lib.)

UNITED STATES PATENT OFFICE CETIFIQATE F CQREG'HQN Patent No 3 ,l2l ,008 February 11 1964 Jean E. Jones et al.

t error appears in the above numbered pat- It is hereby certified tha etters Patent should .read as ent requiring correction and that the said L corrected below.

Column ll, line 9, for "R read R column 13, lines 49 to 55, for the lower righthand portion of the formula reading \CH read \CN Signed and sealed this 10th day of May 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDW 1 J. BRENNER 7 Commissioner of Patents Attesting Officer 

1. A PHOTOCONDUCTIVE COMPOSITION COMPRISING SENSITIZED PHOTOCONDUCTIVE ZINC OXIDE PARTICLES UNIFORMLY DISPERSED IN A HIGH DIELECTRIC, ORGANIC BINDER-INSULATING MATERIAL FOR SAID ZINC OXIDE, SAID ZINC OXIDE BEING SENSITIZED WITH A DYE SELECTED FROM THE CLASS REPRESENTED BY THE FOLLOWING GENERAL FORMULA: 